It's a lot of work
I've made 2 and it is a lot harder than it may 1st appear. Mine were both based on the Sebak approach and used modifed OMER footpockets. Working with carbon and epoxy resins is not for the faint hearted and at the end of the day cost me not much less than what you can buy off the shelf.

Key challenges are:
- layering the glass effectively (by hand)
- getting the layering quantities right for the performance you desire
- consolidating the resin by hand so that it gives as close as possible a finish to vacuum bagging
- fixing the footpockets effectively once complete.
I've seen some plain monofins made out of a sheet of plastic that work ok, but having made my own, bought a SEBAK and now a WaterWay mono, I'll be sticking to the Waterway from this point forward.....awesome and well priced.... and after all if it's good enough for Carlos and a bunch of other legends it will sure do me.